(1) Field of the Invention
The present invention relates to a molded type semiconductor device, and more particularly to a molded type semiconductor device and a lead frame of a molded container which are used in the microwave band region.
(2) Description of the Related Art
As conventional microwave band semiconductor devices, there are those which are constructed by ceramic receptacles and those which are constructed by mold resin receptacles. In the former type, as shown in FIG. 1, a lead frame 22 is soldered to a ceramic receptacle 21, and the semiconductor chip 23 mounted in the ceramic receptacle 21 is electrically connected to the lead frame 22 by wires 24. Further, the semiconductor chip in the circuit is grounded by the connection established through a grounding lead 25 to a grounding portion 27 by, for example, solder 28, provided on a dielectric base plate 26 and by the connection established via a through-hole 29 to a grounding metal film 30. In this way, the grounding can be made with the shortest distance to the ground and the lowest impedance with almost no adverse influence to the circuit. However, the disadvantage therein is that the receptacle becomes structurally complex and costly.
In the latter of the types explained above, as shown in FIG. 2, a semiconductor chip 32 is mounted on a grounding lead 31a of a lead frame 31 with the electrical connection being made therebetween by a wire 33 and, after the other electrode is connected to the other lead 31b by a wire 34, the molding is made using a resin 35. For the grounding of the semiconductor chip 32, the connection is made through the wire 33 and the grounding lead 31a to a grounding portion 37 by solder 38 and through a through-hole 39 to a grounding metal film 40. The advantages in this arrangement are that the receptacle can be made simpler in its structure and less costly in its manufacture as compared with that of the former type. However, since it is difficult to make the length of the grounding lead 31a short, the grounding impedance inevitably becomes large. Thus, the mold type semiconductor device of the kind explained suffers from a deterioration of circuit characteristics in microwave band regions.
For the grounding in a circuit, use of a stub and a capacitor has been proposed in, for example, Japanese Patent Application Kokai Publication No. Hei 3-198402. This proposed configuration is shown in FIGS. 3A and 3B. Here, a circuit substrate 41 is multi-layered and consists of a plurality of insulating layers 42 and a plurality of conductive layers 43. As a part of the circuit, an open end stub 44 is formed and is connected to a part of one of the conductive layer 43. Thus, the grounding is established when the semiconductor chip is mounted on the circuit substrate 41 and the grounding electrode is connected to the open end stub 44.
However, although the foregoing configuration is effective in a hybrid integrated circuit device of the type in which the semiconductor chip is mounted directly in a circuit substrate, there is a difficulty in applying such a configuration to a discrete type semiconductor device as described above.
As shown in FIG. 4A, by connecting a power source electrode of a semiconductor chip 51 to a chip capacitor 53 by a wire 52 and connecting the chip capacitor 53 to a substrate 55 by a wire 54, it is possible to accomplish the grounding of a high frequency component at a node A of the capacitor 53 as shown in FIG. 4B. Here, L.sub.1 and L.sub.2 denote parasitic inductances of the wires 52 and 54, respectively. In this example, use of the chip capacitor 53 increases the number of component elements, hence increasing the cost involved. Also, in the case where this structure is to be sealed in a receptacle, there is no alternative but to use a ceramic receptacle in order to make the grounding of the capacitor 53, which complicates the structure and adds to the cost.
Thus, when a semiconductor device is fabricated using a conventional ceramic receptacle or a conventional external circuit, there will be a problem in that the structure becomes complex and requires a larger number of component elements, resulting in a higher manufacturing cost.
In the case where a conventional molded receptacle is used in the fabrication of a semiconductor device, there will be a problem in that the impedance of a lead at a microwave band region becomes large and makes the grounding difficult, resulting in deterioration of circuit characteristics.